Butter bottom and sides of a 9-inch square pan; add some fine dry bread crumbs and shake pan until coated.
Set pan aside.
Cook macaroni according to package directions; drain.
Beat 3 eggs with the garlic salt and pepper thoroughly in large mixing bowl; stir in ricotta and Parmesan cheeses.
Squeeze out excess water from spinach; add with macaroni to cheese mixture.
Blend thoroughly.
Turn mixture into prepared pan; smooth surface with spatula.
Beat remaining egg in small bowl; brush on top of mixture with pastry brush.
Bake at 350° 25 to 30 minutes, or until knife inserted in center comes out clean.
Run a small spatula around sides of panto loosen; cut into 36 squares, 1 1/2 inches, as appetizer, or larger squares for mealtime accompaniment.